A traveling-wave tube, a klystron, and the like are electron tubes used to amplify and oscillate a radio frequency signal through the interaction between an electron beam emitted from an electron gun and a high-frequency circuit. For example, as shown in FIG. 1, traveling-wave tube 1 is configured so as to include: electron gun 10 that emits electron beam 50; helix electrode 20 that is a high-frequency circuit that causes electron beam 50 emitted from electron gun 10 to interact with a radio frequency signal (microwave); collector electrode 30 that acquires electron beam 50 outputted from helix electrode 20; and anode electrode 40 that extracts electrons from electron gun 10 and, at the same time, guides electron beam 50 emitted from electron gun 10 to spirally-shaped helix electrode 20. Electron gun 10 includes: cathode electrode 11 that emits thermal electrons; and heater 12 that supplies cathode electrode 11 with thermal energy for emitting thermal electrons.
Electron beam 50 emitted from electron gun 10 is accelerated by a potential difference between cathode electrode 11 and helix electrode 20, introduced into helix electrode 20, and progresses through the inside of helix electrode 20 while interacting with a radio frequency signal inputted from one terminal of helix electrode 20. Electron beam 50 having passed through the inside of helix electrode 20 is acquired by collector electrode 30. At this point, a radio frequency signal amplified by the interaction with electron beam 50 is outputted from another terminal of helix electrode 20.
Power supply 60 includes: helix power circuit 61 that supplies cathode electrode 11 with helix voltage Vhel that is a negative direct voltage with respect to potential HELIX of helix electrode 20; collector power circuit 62 that supplies collector electrode 30 with collector voltage Vcol that is a positive direct voltage with respect to potential H/K of cathode electrode 11; and heater power circuit 63 that supplies heater 12 with heater voltage Vh that is a negative direct voltage with respect to potential H/K of cathode electrode 11. Helix electrode 20 is normally connected to a case of traveling-wave tube 1 and is grounded inside power supply 60.
While FIG. 1 shows a configuration example of traveling-wave tube 1 including one collector electrode 30, traveling-wave tube 1 may alternatively be configured so as to include a plurality of collector electrodes 30. In addition, while FIG. 1 shows a configuration in which anode electrode 40 and helix electrode 20 are connected inside power supply 60, a case is also possible where anode voltage Va that is a positive direct voltage with respect to potential H/K of cathode electrode 11 is supplied to anode electrode 40.
Helix voltage Vhel, collector voltage Vcol, and heater voltage Vh can be generated by, for example, a configuration that includes a transformer, an inverter that converts an externally supplied direct voltage into an alternating voltage and that supplies the alternating voltage to a primary winding of the transformer, and a rectifier circuit that converts an alternating voltage outputted from a secondary winding of the transformer into a direct voltage.
Meanwhile, a conceivable method of measuring a current flowing through a high-voltage site such as cathode electrode 11, collector electrode 30, heater 12, and the like in traveling-wave tube 1 shown in FIG. 1 involves inserting an ammeter in series between a measurement object electrode and a power circuit that supplies a predetermined direct voltage to the electrode.
However, with the method using an ammeter, since high voltage is also applied to the ammeter that measures currents flowing through cathode electrode 11, collector electrode 30, and heater 12 which operate at high voltage (several kVs to several tens of kV), measures such as insulating the ammeter need to be taken so as to ensure that the measurement operation is conducted in a safe manner. In addition, since an ammeter is normally used only when testing traveling-wave tube 1 or power supply 60, currents cannot be constantly monitored.
In consideration thereof, a method is conceivable in which current sensor 70 including a hall element or the like is fixed to, for example, wiring connecting cathode electrode 11 and helix power circuit 61, whereby flux generated when a current flows through the wiring is detected and the detected flux is converted into a current value.
However, current sensor 70 that detects a current using flux is disadvantageous in that current sensor 70 is also unintentionally affected by a peripheral magnetic field which makes it difficult to detect a small current. In addition, the fact that current sensor (hall element) 70 is generally expensive raises the cost of the entire high-frequency circuit system including traveling-wave tube 1 and power supply 60.
Japanese Patent No. 2711897 discloses a configuration for detecting an operating current of a traveling-wave tube in which a dedicated transformer for current detection (hereinafter referred to as a current-detecting transformer) is included in a power supply.
The power supply described in Japanese Patent No. 2711897 includes: a power supply transformer; an inverter that supplies power to a primary winding of the transformer; and a rectifier circuit that rectifies an alternating voltage outputted from a secondary winding of the transformer and generates a power voltage to be supplied to a cathode electrode and a collector electrode of a traveling-wave tube, and is configured such that a primary winding of a current-detecting transformer is inserted in series between the secondary winding of the transformer and the rectifier circuit. In such a configuration, a signal indicating a value substantially equal to a current flowing through the cathode electrode of the traveling-wave tube can be obtained from the secondary winding of the current-detecting transformer.
As described above, in the method of detecting a current using a current sensor, there are problems in that a small current is difficult to detect and that in the expensiveness of the current sensor (hall element) raises the cost of the entire high-frequency circuit system including the traveling-wave tube and the power supply.
Meanwhile, as described above, since the power supply described in Japanese Patent No. 2711897 is configured such that the primary winding of the current-detecting transistor is inserted in series between the secondary winding of the transformer and the rectifier circuit, a signal outputted from the secondary winding of the current-detecting transistor includes not only a value of the current flowing through the cathode electrode of the traveling-wave tube but also values of currents consumed by the current-detecting transistor and the rectifier circuit. Therefore, in the configuration described in Japanese Patent No. 2711897, it is hard to say that a current flowing through the cathode electrode of the traveling-wave tube is properly measured.
In addition, since the power supply described in Japanese Patent No. 2711897 uses a relatively expensive current-detecting transformer capable of also operating at high voltage (several kVs to several tens of kV), the cost of the entire high-frequency circuit system including the traveling-wave tube and the power supply rises.
Furthermore, the power supply described in Japanese Patent No. 2711897 is incapable of measuring a current flowing through electrodes other than the cathode electrode.